Recording system



April 13, 1937. E. c. WENTE I RECORDING SYSTEM Filed Dec. 4, 1935 OUUUOOUOOUG /NVE/VTOR E. C.WE/V7 E TO RNE Y accordance with the signal currents.

Patented Apr. 13, 1937 PATENT OFFICE RECORDING SYSTEM Edward C. Wente, New York, N. Y.,assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New Yorkv Application December 4, 1935, Serial No. 52,915

V 8 Claims.

This invention relates to film sound recording systems and particularly to systems in which two complete complementary records of the sound waves are produced in one sound track.

The object of the invention is a film sound record in which the undesired noise due to irregularities in the recording material is substantially reduced and in which, when reproduced, the undesired frequencies due to distortion of the wave form will be substantially neutralized. A feature of the invention is the method of producing with a single devicetwo complete complementary sound wave representations and simultaneously limiting the area of the film from which the ground noise may be produced.

Another feature of the invention is a sound record in which the sound is recorded as a series of laminae of equal length, laterally displaced from the center line of the sound track, and in which the transparent area of the sound record is at all times as small as possible.

Sound recording systems are known in which the original or negative record is respectively exposed from the two marginal edges inward to form two complete complementary sound wave representations. In the systems heretofore known, such as the system shown in U. S. Patent 1,833,373, two separate light sources were used respectively to produce the two exposures on the marginal edges of the sound track. As the two' channels leading to the recording light and the recording lights themselves rarely have identical characteristics, the two records produced are not usually identical in shape. A certain measure of distortion is thus produced by this recording method. Also, when recording sounds of small amplitude by such a recording system, substan'-" tially one half of the record produced istrans- I parent and as the transparent areas of the' film. tend to give rise to undesired noise upon repro duction, the undesired noise from such a film is unduly large.

In the present system of recording an opaque conducting ribbon is placed in the recording beam of light having its longer axis aligned with the longitudinal axis of the film. An image of the ribbon occupying substantially one half the width of the sound record is formed upon the film. The conducting ribbon may be oscillated laterally in Two other conducting ribbons are respectively stretched on opposite sides of the central ribbon in the record track. The two outer ribbons are moved laterally of the film in accordance with the envelope of the amplitude variations of the signal currents and thus limit the exposed area of the original or negative film to the least amount which will carry the modulation of the center ribbon.

The film produced by the present recording system comprises in the original or negative record a central unexposed area of constant width which is varied in position laterally of the sound track in accordance with the variations in the signal current, an exposed area on both sides of the central unexposed area, and two unexposed areas respectively extending from the marginal edges of the record track very close to the unexposed'areas in the center of the track. The exposed area of the original or negative record is thus as small as possible. When a reproduction sound record is printed of such an original or negative record, the exposed areas of the reproduction prints willbe as large as possible, the transparent areas of the reproduction prints consequently being as small as possible. Thus, when such a record is reproduced,the ground noise arising from the transparent areas of the reproduction prints will be a. minimum.

In the drawing, Fig. 1 is a diagrammatic representation of a sound recording system embodying these inventions;

Fig. 2 is a fragmentary enlarged view of a light valve adaptedfor use in the system of Fig. 1;

Fig. 3 is a representation of the original or negative film sound record produced by the recording'system' of Fig. 1.

Fig. 4 is a representation of a positive print of the record shown in Fig. 3.

In'Fig'. 1 the microphone I and amplifier 2 form a" source of electric waves modulated in accordance' with a desired signal. Any other source of modulated signal waves may be used, such as a phonograph pick-up, a radio receiving set, a telephone line, etc. The modulated signal wave may be further amplified in amplifier 3 and supplied through a transformer 4 to a conductive ribbon 5 immersed in a constant magnetic field. The magnetic field produced by the current flowing in the conducting ribbon 5 will react with the constant magnetic field to produce a lateral oscillation of the ribbon 5.

A constant current from a battery 8 flowing through an inductor 9 and a resistor It is supplied through the wire I I to a pair of conductive ribbons 6 and I connected in serial relationship and disposed on each side of the conductive ribbon 5 and. in the same magnetic field. The ourrent flowing through the ribbons 6 and l returns through the wire I2 to the battery 8.

A portion of the modulated currents from the amplifier 3, further amplified, if desired, in the amplifier l3 are supplied through the transformer M to the bridge type'full-wave rectifier IS. The output of the rectifier I5 charges up the capacitor !6. The charge on the capacitor l6 will tend to flow through the resistor-IT, inductor l8, resistor ii and inductor 9 thus opposing the flow of current from the battery 8. The above elements constitute a well-known form of noise reduction circuit similar to that disclosed in U. S. Patent 1,923,757 patented August 22, 1933 to H. C. Silent. The present invention is in no way limited to the specific type of noise reduction circuit disclosed as any other type of circuit which will produce a current varying in accordance with the envelope of the amplitude variation of the signal current may be substituted for the circuit shown.

In the absence of sound the constant current from the battery 8' flowing through the ribbons 6 and I is adjusted to draw the ribbons 6 and 1- very close to the ribbon 5. When signal curstructurally similar-to the light valve disclosedin my previous Patent 1,914,186 patented June 13, 1933 to E. C. Wente exoeptthat'the light valve has three ribbons in place of two and the ribbons are disposed parallel to the longitudinal axis of the sound record. In Fig. 2 the member 19:

corresponds to the support 1 disclosed in my patent. The ribbons 5, 6 and I are disposed at right angles to the small orifice 20 pierced in the member 19. The ribbons 6 and T are stretched in their proper position and attached.

to suitable supports, such as 2| and 22. The ribbon 5 may be similarly stretched and attached to a support 23 which is recessed so as not to interfere with the movement of the ribbons 6 and 1'. As the ribbon 5 operates on much higher: frequencies than the ribbons 6 and I, the ribbon 5 may be much shorter in length, and maybe ten:- sioned to resonate at a higher frequency than ribbons 6 and l.

In Fig. 1 light from the source 24 is focused by the lens system 25 on' the small orifice 20 pierced in the support IS. The light transmitted through the orifice 2B is focused by'the lens 26 on the record track of a photographic film 21. moved through the beam at uniform speed in a known manner.

The two edges of the ribbon 5 imaged upon the moving film 21 will define the two. lines of: exposure 28 and 29 shown on Fig. 3. When signal currents are applied to the ribbon 5- causing the ribbon to oscillate laterally of the film 21 the: lines 28 and 29 will vary laterally ofthe film in position or alignment but are at all times spaced the same distance laterally of the film from each other. The edge of the ribbon 6 imaged upon the film 21 will form a line serving to define an unexposed area extending inward from the marginal edge of the sound track and varying in width inversely in accordance with the envelope of the amplitude variations of the signal. The edge of the ribbon I imaged upon the film 2.7.

forms a line 3| similar to the line 30. The exposed area of the original or negative film is thus at all times as small as possible. Thus when a reproduction sound record is. printed of such an original or negative record, such as shown in Fig. 4, the exposed area of the reproduction print will be as large as possible thus reducing the transparent areas of the reproduction print from which the ground noise arises during, reproduction. The corresponding lines in Figs. 3 and 4 have been designated by the same numerals.

The positive or reproduction print shown in Fig. 4: may be reproduced by two separate channels, as shown in U. S. Patent 1,833,373, or by a bridge arrangement connected to a single channel, as shown in U. 5. Patent 1,879,423, or by the beam splitting arrangements shown in British Patent 332,197 or French Patents 713,816 and 773,532.

What is claimed is:

1. A positive photographic record of sound comprising an exposed area substantially one half the width of the record track, centrally disposed in the record track and laterally displaced in accordance with the variations in the sound and two exposed areas respectively disposed in the mar--- ginal edges of the sound track and varying in width inversely in accordance with the envelope ofthe amplitude variations of the sound.

2. The method of recording sounds upon a photographic sound track which. comprises projecting light upon an opaque element having its axis aligned with the longitudinal axis of the sound track, forming an-image'of, said element upon the sound track, said image occupying, substantially one half the lateral width of the sound track,. laterally oscillating said element in accordance with the sound to be recorded, respectively defining the two margins of the light impressed upon. the sound track ,by means; of two elements having their axes aligned with the 1ongitudinal axis of the sound track and laterally displacing said. last two elements in accordancewith the envelope of the amplitude variations of the sound.

3; A negative photographic; record of a modulated electric current comprising an unexposed; area substantially one half the width of the rec- 0rd track. and laterally displaced in accordance with the variations in the modulated electric currents and two unexposed areas respectively disposed in the. marginal edges of thesound track and varying in width. inversely in. accordance:v

with the envelope of the amplitude variations of: the: modulated electric current.

4. A negative record of a modulated electric current comprising an unexposed area of substantially constant width centrally disposed-in the record track. and, laterally displaced inaccordance with the variations in the modulated electric current and two unexposed areas respectively disposed in the marginal edges of the soundtrack and extending inwardly substantially to the envelope of thevariations in the central unexposed area.

5. The method of recording a modulated electric current upon. a photographic film which comprises projecting a narrow beam of light having its longer axis transverse to the axis of the film upon an. opaque element. having its axis aligned with the longitudinal. axis of the film, forming an imageof said element upon the film occupying substantially one half the lateral width of the sound track, laterally oscillating said element in accordance with the modulated electric current,

respectively defining the two margins of the light beam impressed upon the film by means of two opaque elements having their axes aligned with the longitudinal axis of the film and laterally displacing outward said last two opaque elements in accordance with the envelope of the amplitude variations of the modulated electric currents.

6. In a system for recording modulated electric currents in combination, a photographic film moved at constant speed, an opaque plate pierced by a small orifice having its longer axis transverse to the axis of the film, a source of light, a lens system for focusing light from said source to illuminate said orifice, magnetic means for forming a constant magnetic field including said orifice, a lens system for forming an image of said orifice upon said film, an opaque conducting ribbon having its longer axis parallel to the axis of the film centrally located in the light from said orifice and immersed in said magnetic field, a source of modulated electric current, means for supplying current from said source to said ribbon to cause said ribbon to oscillate laterally of the film in accordance with the variations in the modulated electric current, a pair of opaque conducting ribbons respectively disposed on each side of said first ribbon and parallel thereto, means for supplying a constant current to said two ribbons to limit the width of said image impressed upon said film and a detector for deriving an electric current varying in accordance with the amplitude variations of said modulated electric current and connected to nullify the effects of said constant current on said two last named ribbons.

7. A positive photographic record of sound comprising an exposed area of substantially constant width centrally disposed in the record track and laterally displaced in accordance with the variations in the sound and two exposed areas respectively disposed in the marginal edges of the sound track and varying in width inversely in accordance with the envelope of theamplitude variations of the record.

8. The method of recording a modulated electric current upon a photographic film which comprises projecting a narrow beam of light upon an opaque element, forming an image of said element of substantially constant width laterally on said film, laterally oscillating said image by and in accordance with the variations in said current, respectively defining the two margins of said beam impressed upon said film, and laterally displacing said margins in accordance with the envelope of the amplitude variations in said current.

EDWARD C. WENTE. 

